Freshly isolated, dark-adapted photoreceptors of vertebrate retinas are measured in side-on orientation for their absorption of linearly polarized light. Rod outer segments of mudpuppy, larval and adult tiger salamanders and tropical toad contain approximately the same in situ visual pigment concentration. This, in turn, supports the hypothesis of invariance of oscillator strength within each of the two families of visual pigments. The shapes of absorption spectra of the rhodopsins and the prophyrosins vary according to lambda max. However, the product of spectral bandwith and molar extinction coefficient appears to have a characteristic value for each pigment family. Cone cells of the goldfish retina are investigated for morphological markers so that the three types of pigments contained in them may by be related to their connections with other neurons. This study is aimed to reveal how this retina processes color information. The technique of microspectrophotometry is also applied in the study of gene expression in mouse leukocytes. Such tissue-cultured cells can be induced to synthesize hemoglobin. The amount of hemoglobin a cell makes and the frequency of cells so triggered in certain clones are indicative of the control processes of erythroid differentiation.